The invention applies to telecommunication systems using a transmission technique termed Frequency Division Multiple Access, this technique being known by the acronym FDMA.
Transmission or reception of signals via a satellite is done by means of connection stations (gateways) distributed over the surface of the Earth. To allow access by broadband transmission systems, the connection stations are overdimensioned in the radiofrequency (RF) part and consequently have a high cost. Despite this, most budgets show that the uplink (transmit direction) retains a non-negligible share of unavailability related to poor atmospheric conditions (rain), in particular for links from 30 GHz upwards.
The potential clients of these systems desire an improvement in the service.
To solve this problem, the Applicant proposes to implement a solution consisting in affording transmit site diversity.
Solutions for implementing diversity already exist for the reception of signals via a satellite.
However the present case deals with implementing site diversity for the uplink, that is to say at the transmit end, thereby posing a particular problem.
Specifically, the demodulators of the terminals operate on a carrier that is assumed to be coherent and continuous. Consequently, any loss of phase synchronization or temporal synchronization induces the equivalent of a cycle jump with a significant packet of errors and this may produce a return to the acquisition mode of the terminal with re-connection of the users.
Thus to implement site diversity at the transmit end in this type of system, the problem identified by the Applicant is the toggling of the signal between two remote sites, the distances of the sites being able for example to be about 5 to 30 km, while ensuring that the carrier has the same lag and the same phase on reception by the terminals. The solution must be able to be applied to carrier frequencies of possibly 30 GHz, optionally 14 GHz (in practice to any carrier frequency). To this end, the invention proposes a solution consisting in using a first and a second remote connection station, in slaving the signals of the first and second connection station so as to toggle from one to the other in the event of heavy rain without loss of the synchronization for the carrier.
The invention does not require any particular implementation at the level of the demodulator of the terminals, complying with the cost constraints related to these markets.